A modern radio telecommunication environment is very diverse with the use of numerous radio communication schemes, both standard and non-standard. User devices may be equipped with capabilities to communicate through multiple different radio communication schemes, e.g. GSM, GPRS/EDGE, Bluetooth, WLAN, UMTS and its evolution versions HSDPA, LTE and LTE-A. Additionally, concepts like cognitive radio or software-defined radio are seen to be implemented in the user devices in near future. Cognitive radio and software-defined radio are general concepts to denote radio devices that are able to sense a radio environment and to select a radio communication scheme and radio communication parameters that are the most suitable for the sensed radio environment.
Support for numerous radio communication schemes operating on different frequency bands sets requirements for radio interface components of the user device. The radio interface components, including analog amplifiers, have to operate linearly over a large frequency band. The linearity requirement on the numerous frequency bands sets challenges to the design of the radio interface components.